What is the minimum thickness for soundboard? If a spruce soundboard has an average thickness of 28mm, can it still be used for a guitar top based on Segovia's Hauser 1937 that has a thickest part of about 31mm? Can we put taller or wider struts by say 2mm for all struts to increase strength? Would the sound be different?

After 1940s, Hauser used a thinner soundboard for a more Spanish methodology, as it was said. Anybody know the thickness range of Hauser guitars after 1940s?

I think you dropped a decimal point. If you made a soundboard 28mm thick (that's over an inch) even Segovia would have a hard time getting it to sing! Surely you meant 2.8mm and 3.1mm, no?

But in general I think there are always a whole range of combinations that work...thinner soundboard with extra braces, thicker soundboard with thinner braces, add in various convolutions of neck-angle and string height not to mention plantilla and the possibilities are legion. For instance, my old Sakurai/Kohno has a very high string height which combines with a not particularly thick Cedar soundboard to let them use a rather substantial Fleta-inspired bracing style and still get a very open and responsive instrument. Doesn't sound at all like a Fleta, that oddball set of geometric choices creates its own voice.

You could certainly use that wood, but your success would be higher if you chose a model that used that thickness, or less, already. Torres used soundboards not thicker than 2.8mm, and Bouchet kept his closer to 2mm.

Thanks Brent. I was thinking 2.8mm but typing 28mm. Yes of course what I meant was a decimal point in mm.

Well, for a start, this luthier based in Bandung - Indonesia started guitar making from scratch. But his optimism and eagerness to learn keeps his luthierie well-being until present. I have been supplying him with a lot of materials and 'things that I picked up from the net' for his necessities. He never atttended any guitar-making course, simply he couldn't afford it. His progress in guitar making is quite convincing except there are issues that he cannot comprehend. Lack of practical knowledge and formal training I suppose.

So I try to assist him to use that soundboard which is not easily available here in Indonesia. Anyway, thanks about your advice and I would encourage him to use that soundboard with a taller struts. See what happens.

Why not just buy Brunes plan from GAL? That's probably the only way you are going to get a fairly accurate copy of a Hauser without having the original on the bench. Not only that but compared to many Museum plans GAL offerings are very reasonably priced.

There is some discussion in "Making Master Guitars" by Roy Courtnall, pp. 62-63. He writes that after 1940 Hauser's guitars were very much like Torres' guitars, especially the "domed" soundboard. The dome structure gives the soundboard additional strength: "This inherent strength means that the soundboard can be worked quite thin, without any danger of it collapsing in front of the bridge." Hauser also owned a Torres guitar built in 1860. It seems (same book, but based on Romanillos) that the Torres guitars had rather thin soundboards: 2.5 mm around the soundhole, but "thinning out" to only 1.4 mm in the peripheral area. So I think that the pressure exerted by the bouts onto the soundboard also is really crucial here (M. Rodriguez mentions this also in the Introduction of his book).

So I guess you have to take care of the "domed" structure and to use a rather thin soundboard, and to check also about the bouts, but I actually wonder whether you can get this precise information from some plans.

There is some discussion in "Making Master Guitars" by Roy Courtnall, pp. 62-63. He writes that after 1940 Hauser's guitars were very much like Torres' guitars, especially the "domed" soundboard. The dome structure gives the soundboard additional strength: "This inherent strength means that the soundboard can be worked quite thin, without any danger of it collapsing in front of the bridge." Hauser also owned a Torres guitar built in 1860. It seems (same book, but based on Romanillos) that the Torres guitars had rather thin soundboards: 2.5 mm around the soundhole, but "thinning out" to only 1.4 mm in the peripheral area. So I think that the pressure exerted by the bouts onto the soundboard also is really crucial here (M. Rodriguez mentions this also in the Introduction of his book).

So I guess you have to take care of the "domed" structure and to use a rather thin soundboard, and to check also about the bouts, but I actually wonder whether you can get this precise information from some plans.

Best wishes,

jorpheus

You can get a lot of precise information from Plans, but then again that depends on who drew up the plans and how much access they had to the instrument. I can't comment on the GAL Hauser plan because I don't own it. I do own Elliotts Torres plan and it is very detailed, with soundboard thickness measurements in abundance. Of course a good knowledge of the original makers methods and procedures helps enormously, so the combination of the two is key. The rest is experience of working wood and (possibly) altering dimensions to suit.

Any good luthier will tend to vary the thickness of the soundboard depending on the wood that he's using. That 3.1mm thickness was what Hauser figured would work with that piece of spruce, and he was right. He might have used a different thickness with another piece of wood.

The main consideration in figuring top thickness is getting enough stiffness to resist the long-term pull of the strings and keep the top from dishing too much in front of the bridge. If you have a piece of wood that is very stiff along the grain you can make it thinner, and if it's not as stiff, leave it thicker. One interesting point in this is that the stiffness along the grain (as measured by the Young's modulus) tends pretty well to track with the density. Since the actual stiffness of the piece will depend on the Young's modulus and the cube of the thickness, using a low density piece of wood and leaving it thicker tends to result in a lighter soundboard. This is good, because the energy in the strings is pretty limited, and a lighter soundboard will be easier to drive.

Traditionally one learned in the course of making a bunch of instruments what a soundboard should feel like when it's flexed. It takes a while to gain this skill, and some folks are much better at it than others. Lately some makers have developed objective tests for these things. Common ways are to look at deflection under a standard load, or to find the resonant mode frequencies of the top blank, which, along with the dimensions and weight, can be used to derive the Young's modulus and density. You might be surprised at how variable any one species of spruce is in terms of density and Young's modulus! At present you still have to do a lot of testing to develop your own data base and figure out what it means, but hopefully in the future more of this information will be available.

Classical guitar designs often seem to fall into two camps; ones that use a thick soundboard and ones that use a thin one. Hauser tended, in my understanding, to use a thicker soundboard than some of the Spanish makers. Each different gutiar design has to be approached as a system. If you're copying Hauser, then use a soundboard that is on the thick side, but be aware that there's nothing holy about 3.1mm per se.

On the plans for Segovia's 1937 Hauser, drawn by R.E. Brune (c. 2003), there is an area near the tail block on the treble side that is listed as 3.24mm thick. Moving toward the treble side lower bout, it tapers to 3.08mm then 3.01mm. However, this is not the typical thickness of the top. On the bass side lower bout, the thickness is only 2.21mm. In general, the thickness varies widely over the whole top, with an overall "average" of perhaps 2.6-2.7mm.

I've often wondered, when I see historical plans with a lot of variation in top and back thicknesses, whether the variations are carefully and cleverly designed to exploit the properties of the particular piece of wood, or maybe just what the luthier felt was good enough in the absence of modern highly accurate digital thickness gauges.
Robert

What is missing in this discussion of soundboard thickness is the other equally important part of the top design, the bracing. I don't know how you can have a complete, meaningful discussion of top thicknesses without taking into consideration the whole design of the top. To say you can build a top at 3.1mm or 2mm is only part of the story. I've seen several Hausers that were a full 3mm in some areas, with extremely light bracing. It not simply a given that one is going to brace the top-the design and details of the bracing are extremely important when discussing top thickness. IMO. Comments?
p

sdluthier wrote:What is missing in this discussion of soundboard thickness is the other equally important part of the top design, the bracing. I don't know how you can have a complete, meaningful discussion of top thicknesses without taking into consideration the whole design of the top. To say you can build a top at 3.1mm or 2mm is only part of the story. I've seen several Hausers that were a full 3mm in some areas, with extremely light bracing. It not simply a given that one is going to brace the top-the design and details of the bracing are extremely important when discussing top thickness. IMO. Comments?
p

You're right-on Peter. The original poster mentioned something about Hauser (notably thick soundboards), but that could have been an isolated piece of info. I was discussing this on the phone with another luthier today. ... It is usually not a single variable, like thickness, that determines the quality of the outcomes, but a combination of factors... A configuration or system.
In the Hauser system, a thicker soundboard is typical. The one I measured recently was 3.0 over most everywhere, except the wings of the lower bout.

Thanks to all about your advice. I have read Roy Courtnall, Torres by Jose Romanillos and the 1937 Hauser plan. Actually what I was about to do (in co-operation with a local luthier) is to copy Hauser 1937 just for try-out, not to seek a certain quality guitar based on that plan. The first try was ok, but again that luthier was lack of many issues and we would like to explore further.

Now for the second try, we would make another copy of 1937 Hauser using one of the best spruce he's got, except he pared down to about 2.8mm before tuning it and putting some braces on. Hauser plan has a thickness of more than 3.00mm being 3.24mm as the thickest part. So that was how the topic derived: whether a soundboard of 2.8mm can be used for that particular plan. We all know that there are many factors that contribute to a quality sound for good guitars. We thought of using the soundboard we've got. To compensate the thinner part of the soundboard, we were thinking to increase the height or the width by ,say, 0.2mm to increase the strength, or maybe not.

We talked about dooming and flexing the soundboard which is one of the potential solution for thinner soundboard. Again, I amnot a luthier, that local luthier is more or less an amateur luthier when we get to master guitars level. So I need to explore these issues further. The best way is by practising it. I just don't have any guidance how to do it.

Anyway, I am grateful that I could have the discussions here at Delcamp forum with very valuable comments and advices for all of you.

VOL.2003;NO.;PAGE.253-254(2003)
Figure&Table&Reference;FIG.5, TBL.1, REF.5
Pub. Country;Japan
Language;Japanese
Abstract;Braces on Soundboard of acoustic guitar have an influence on sound quality. Usually, the bracing location depends on guitarmaker skill and feeling. This paper describe a relationship between the bracing pattern, board thickness and vibrational characteristics of a sound board, analytically. The following results were obtained: (1) Amplitude level is not always proportional to soundboard thickness. (2) Reducing the thickness of soundboard and increasing the number of braces are good for enlargement of antinode area. (author abst.)

Plans are useful for getting the geometry part, and for learning the graduation system (if there's any), but you should definitely not copy the thickness exactly. You do not know the density and the stiffness of the original. I imagine you don't even know that about your own top, so, unfortunately having to be blunt, nobody can help you over the internet. It is frustrating and it has stressed me for 1 year while I worked on my first two top voicing processes. Now having almost 6 under the belt, the puzzle somewhat starts to look like it will come together and i feel more confident about the future builds.

Btw should I mention you also do not know the density of the bridge? Rosewood varies too and you can get important tone changes from simply switching between different weight bridges.

This being said, 0.2 mm difference over a small area only is almost nothing especially if not in the center between bridge and soundhole . Go ahead and build with it.

RobertE: "or maybe just what the luthier felt was good enough in the absence of modern highly accurate digital thickness gauges." This was my case with my first guitar. I thinned the top with a plane and did some graduations after it was completed. I had nothing to measure it, except the edges with a regular caliper. Later I bought a Hacklinger caliper and the variation in thicknesses was quite complex, really almost impossible to copy if someone would want to.

I would say that these very small variations are not necessarily going to make some secret voicing pattern, but rather giving some character to the guitar. Not better or worse, just a little different.